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Name: Aal
Status: Other
Grade: Other
Location: NJ
Country: United States
Date: November 2007


Question:
When designing a water bridge, does the bridge have to be designed to withstand the additional weight of ship and barge traffic, or just the weight of the water?



Replies:
Hi Aal,

In a water bridge, such as the amazing one that was recently opened in Germany shown in the photo here...

http://www.funonthenet.in/content/view/223/31/

...the bridge only needs to withstand the weight of the water. This is because when a boat floats on water, it displaces its own weight of water. That means, that the volume of water that the hull replaces, weighs exactly as much as the boat does. The water that the hull displaces, is replaced by a boat that weighs exactly as much as the water used to.

Regards,

Bob Wilson


The simple answer is that no, a ship will simply displace its own weight of water and no extra weight needs to be supported by the bridge.

Engineering structures are designed typically with many other considerations in mind besides the normal weight to be carried. For example, structures typically have a "safety factor." A safety factor of three, for example, means that the structure will actually support three times the design load without actually failing. Other important considerations for bridges (and buildings) are wind loading and earthquakes. So a full answer to this question would require the expertise of a civil engineer familiar with such projects.

Robert Erck



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